Most wheelchairs are of the foldable type so that they can be readily stored in the trunks of automobiles and the like. Normally, all that is necessary is that the seat and back rest be of flexible canvas material so that they can fold, the main wheels of the wheelchair then being brought close together in side-by-side relationship. In this repect, the wheelchair frame itself generally includes crossed tubular members which can be scissored together when the wheelchair is in its collapsed or folded state.
While the foregoing folding operation reduces substantially the effective width of the wheelchair for storage purposes, the overall height of the chair as measured from the bottom of the main wheels to the upper hand grips on the back rest portion remains the same or in many instances is increased as a consequence of the scissoring action of the main frame structure. Attempts to avoid increasing the overall height of the collapsed chair have taken the form of providing telescoping crossed tubes for the main frame structure which will permit a scissoring action without increasing to any appreciable extent the referred to height.
Another means for rendering the chair more compact in the height direction would be to provide a removable back structure wherein the back tubes and hand grip portions could be removed thus greatly reducing the overall height when the chair is in collapsed position. While the problem is solved by the provision of a removable back, other problems are introduced. Principal among these problems is that of making certain a secure coupling is achieved when the back rest is reassembled on the wheelchair.
It will be appreciated with respect to the foregoing that when a wheelchair is operated by an attendant or nurse, the movement thereof is transmitted through the hand grips on the back rest structure. When the chair is manipulated over ridges or up and down ramps, large tensions can develop in the back rest frame tubes relative to the remaining frame structure and should the removable coupling means for the back rest fail such that the back rest separates from the main frame structure, disastrous results can occur to the patient in the wheelchair.
In addition to the foregoing problem, the inner coupling means for a removable back rest and wheelchair frame should be simple, economical to manufacture, and avoid bulkiness in its construction. Moreover, it should be easy for an attendant or nurse to operate and most importantly, it should be designed as to virtually render impossible inadvertent separation.